Bug 504803 - Allow maxlogsize to be set if logmaxdiskspace is -1
    
    Both the maxlogsize and logmaxdiskspace parameters are allowed to
    have values of -1.  If you set logmaxdiskspace to -1 and then
    later attempt to set maxlogsize to any other valid value, the
    server rejects the change with an operations error.
    
    The problem is that the two parameters are compared to ensure that
    maxlogsize is not greater and the logmaxdiskspace.  We need to
    skip this check if logmaxdiskspace is unlimited (-1).  I also found
    that we were converting -1 to a smaller negative number when doing
    the MB->bytes conversion.  This causes other validation errors that
    expect -1, but not a smaller negative number.  The fix is to skip
    the conversion to bytes and just set a value of -1.